Surface-modified pyrogenically produced titanium dioxide

ABSTRACT

Surface-modified, pyrogenically produced titanium dioxide which is has the following physico-chemical properties: 
     
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     Surface (m 2  /g)   5 to 120                                           
Stamping density (g/l) 50 to 250                                          
Drying loss (%)        &lt;5                                                 
Annealing loss (%)     3.5 to 15                                          
Carbon content (%)     0.5 to 12                                          
pH                     4 to 10.                                           
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This is a division of application Ser. No. 08/012,160, filed Jan 28, 1993 now pending.

The present invention relates to a surface-modified, pyrogenically produced titanium dioxide.

BACKGROUND OF THE INVENTION

It is known to use powdery toners containing surface-modified pyrogenically produced silicon dioxide in electrostatic developing processes. Various silanes, especially dimethyldichlorosilane, are used for surface modification (See U.S. Pat. No. 3,720,617).

It is also known that pyrogenically produced silicon dioxide waterproofed with compounds of the general formula ##STR1## can be added to positively chargeable resin powders in order to increase their flowability (See published European Patent Application EP-A 0,293,009).

It also is known that a titanium dioxide which has been surface-modified with halogen silanes can be added to electrographic developing powders (See published German patent application DE-A 12 09 427).

Furthermore, Published German Patent Application DE-A 34 26 685 (Canon) teaches the addition of a titanium dioxide to positively chargeable toners in which the titanium dioxide had been treated with simultaneously with the adhesion promoters γ-aminopropyltriethoxysilane and trimethylethoxysilane.

A similarly treated titanium dioxide is described in Published Japanese Patent Application JP-OS 31442 (Nippon Aerosil Corporation).

The known method has the disadvantage that it must use an organic solvent system. Alcohols, hydrocarbons and halogenated hydrocarbons are used as solvents which cannot be completely removed from the reaction product.

SUMMARY OF THE INVENTION

The object of the present invention is to avoid these problems and produce a solvent-free, waterproofed titanium dioxide.

The present invention provides a surface-modified, pyrogenically produced titanium dioxide which is surface modified with a silane mixture consisting of silane A (trimethoxyoctylsilane) and silane B (3-aminopropyltriethoxysilane) having the chemical following formulas: ##STR2##

The surface-modified, pyrogenically produced titanium dioxide has the following physico-chemical characteristics:

    ______________________________________                                         Surface (m.sup.2 /g)   5 to 120                                                Stamping density (g/l) 50 to 250                                               Drying loss (%)        <5                                                      Annealing loss (%)     3.5 to 15                                               Carbon content (%)     0.5 to 12                                               pH                     4 to 10.                                                ______________________________________                                    

The present invention also provides a method of producing the surface-modified, pyrogenically produced titanium dioxide in which the pyrogenically produced titanium dioxide is placed in a mixer and sprayed, with the mixer running, with a mixture of silanes A and B. The silanes and the pyrogenically produced titanium dioxide are mixed after the addition of the silane mixture, and the resulting mixture is tempered at 100° to 150° C., preferably at 115° to 125° C.

The ratio of titanium dioxide to silane mixture can be 0.5 to 40 parts by weight silane mixture per 100 parts by weight titanium dioxide.

The silane mixture can consist of 1 to 99 parts by weight silane A and 99 to 1 parts by weight silane

A mixture can be used with preference consisting of 50±20 parts by weight silane A and 50±20 parts by weight silane B.

A particularly suitable titanium dioxide is P 25 which has been produced pyrogenically from TiCl₄ by flame hydrolysis, in an oxyhydrogen flame, and which has the following physico-chemical characteristics:

    ______________________________________                                                              Titanium dioxide                                                               P 25                                                      ______________________________________                                         Behavior vis-a-vis water   hydrophilic                                         Appearance                 loose white powder                                  Surface according to BET.sup.1)                                                                   m.sup.2 /g                                                                             50 ± 15                                          Average size of the                                                                               nm      21                                                  primary particles                                                              Stamping density.sup.2)                                                                           g/l     ca. 100                                             Specific weight.sup.10)                                                                           g/ml    ca. 3.7                                             Drying loss.sup.3) %       <1.5                                                (2 hours at 105° C.)                                                    Annealing loss .sup.4)7)                                                                          %       <2                                                  (2 hours at 1000° C.)                                                   pH.sup.5) (in 4% aqueous dispersion)                                                                      3-4                                                 SiO.sub.2.sup.8)   %       <0.2                                                Al.sub.2 O.sub.3.sup.8)                                                                           %       <0.3                                                Fe.sub.2 O.sub.3.sup.8)                                                                           %       <0.01                                               TiO.sub.2.sup.8)   %       >99.5                                               ZrO.sub.2.sup.9)   %       --                                                  HfO.sub.2.sup.8)   %       --                                                  HCl.sup.8)9)       %       <0.3                                                Sieve residue.sup.6)       <0.05                                               (according to                                                                  Mocker, 45 μm) %                                                            ______________________________________                                          .sup.1) according to DIN 66 131                                                .sup.2) according to DIN ISO 787/XI, JIS K 5101/18 (nonsieved)                 .sup.3) according to DIN ISO 787/II, ASTM D 280, JIS K 5101/21                 .sup.4) according to DIN 55 921, ASTM D 1208, JIS K 5101/23                    .sup. 5) according to DIN ISO 787 IX, ASTM D 1208, JIS K 5101/24               .sup.6) according to DIN ISO 787/XVIII, JIS K 5101/20                          .sup.7) relative to the substance dried 2 hours at 105° C.              .sup.8) relative to the substance annealed 2 hours at 1000° C.          .sup.9) HCl content is a component of the annealing loss                 

The waterproofed titanium dioxide of the invention has the advantage that it has no solvent components.

It can be used in toners for copiers.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following examples illustrate the invention:

EXAMPLE 1

2 kg P 25 TiO₂ produced pyrogenically from TiCl₄ in an oxyhydrogen flame and exhibiting the data indicated above are placed in a 135 liter Lodige mixer and sprayed with 100 g of a silane mixture consisting of 50 g trimethoxyoctylsilane and 50 g 3-aminopropyltriethoxysilane with the mixer running. The mixture is mixed for an additional 15 minutes. The silanized oxide is tempered for 2 hours at 120° C.

The physico-chemical properties of the surface-modified titanium dioxide are as follows:

    ______________________________________                                         Carrier                   TiO.sub.2                                            Surface           (m2/g)  38                                                   Stamping density  (g/l)   134                                                  Drying loss       (%)     0.2                                                  Annealing loss    (%)     3.5                                                  C content         (%)     3.0                                                  pH                        8.2                                                  ______________________________________                                    

EXAMPLE 2

The titanium dioxide waterproofed according to Example 1 is tested in a positive toner system. The toner system consists of the following components:

    ______________________________________                                         Pigment black Printex 35                                                                            7%                                                        Copy-Blau PR (Hoechst AG)                                                                           3%                                                        Toner resin          90%                                                       ______________________________________                                    

The repeated activation was tested with this toner system and a high charge stability in comparison to the raw toner was found (see FIG. 1).

Copy-Blau PR is a charge regulating agent for positive toners. It is characterized as follows:

Area of application

1. Charge regulating agents for positive toners (1- or 2-component toners for copiers or laser printers)

2. Clearing agents for black toners

Chemical

characterization: triphenylmethane derivative

Thermal resistance: >200 C

Solubility: insoluble in water slightly soluble in organic solvents

The toner resin used is characterized as follows:

    ______________________________________                                                      Unit     Theoretical value                                        ______________________________________                                         Melt flow Index.sup.1)                                                                        g/10 min   5-10                                                 (150° C./2, 16 kp)                                                      Viscosity number.sup.2)                                                                       cm.sup.3 /g                                                                               37-43                                                Weight loss.sup.3)                                                                            % by weight                                                                               <1                                                   Residual monomers.sup.4)                                                                      % by weight                                                                               <0.35                                                Styrene                   <0.25                                                n-BMA                     <0.10                                                Other product properties:                                                      Monomer composition       70% by weight                                                                  styrene                                                                        30% by weight                                                                  n-butylmethacrylate                                  Glass transition          60-65° C.                                     temperature Tg.sup.5)                                                          Average grain diameter.sup.6)                                                                            0.200-0.314 mm                                       ______________________________________                                          (d 50 % RS)                                                                    .sup.1) DIN 53 735, 2/88 edition                                               Specimen pretreatment: Drying at 50° C. oil pump vacuum,                .sup.1) hour or 4 hours drying oven, 50° C.                             .sup.2) DIN 7745, 1/80 edition,                                                .sup.3) IR drier until weight constancy                                        .sup.4) Gas chromatography                                                     .sup.5) DSC method, ASTM D 3418/75                                             .sup.6) DIN 53 734, 1/73 edition, evaluation according to DIN 6 141, 2/74      edition                                                                  

    __________________________________________________________________________     The pigment black Printex 35 is characterized as follows:                      RCF (regular color furnace)                                                    Density: (g/cm.sup.3) 1.8-1.9                                                  __________________________________________________________________________     Product specifications                                                                                DBP Adsorption    Extract                                          Depth of                                                                            Color  (mg/100 g)                                                                              Volatile contents                                                                            Sieve                                       Color                                                                               Strength                                                                              powder beads                                                                            Components                                                                              toluene                                                                             Residue                          Printex 35 RCF                                                                         Class                                                                             M.sub.γ -value                                                                IRB 3 = 100                                                                           Powder                                                                              Beads                                                                              (%)    pH                                                                               (%)  (%)                              __________________________________________________________________________     Frunace Blacks                                                                         RCF                                                                               236  100    42   42  0.9    9.5                                                                              <0.1 0.05                             Prinetx 35                                                                     __________________________________________________________________________                        Further technical data                                                                                    BET                                                         Ashing                                                                              Stamping Density                                                                        Particle                                                                            Surface                                                     Residue                                                                             Powder                                                                              Beads                                                                              Size (nm)                                                                           (m.sup.2 /g)                     __________________________________________________________________________                        Furnace Blacks                                                                         0.3  420  550 31   65                                                  Printex 35                                                  __________________________________________________________________________

The q/m measurement takes place under the following conditions:

98% carrier (spherical ferrite (80-100 m))

2% titanium dioxide according to example 1

Activation: Rolling fixture, 360 rpms in 40 ml glass bottle, weighed portion 40 g, developer 

What is claimed is:
 1. An electrophotographic toner comprising a pigment and a surface modified pyrogenically produced titanium dioxide which has been surface modified with a mixture of silane A and silane B corresponding to the chemical formulas: ##STR3## said surface-modified, pyrogenically produced titanium dioxide having the following physico-chemical properties:

    ______________________________________                                         Surface (m.sup.2 /g)   5 to 120                                                Stamping Density (g/l) 50 to 250                                               Drying loss (%)        <5                                                      Annealing loss (%)     3.5 to 15                                               C content (%)          0.5 to 12                                               pH                     4 to
 10.                                                ______________________________________                                     